1. Field of the Invention
The invention relates to electronic/optical communications, namely, the processing of SONET/SDH signals.
2. Description of the Related Art
A framer/mapper/multiplexor (FMM) device is an integrated communications device that converts one or more incoming signals into one or more outgoing signals. For example, an FMM device may convert two or more incoming low-speed signals into a corresponding outgoing high-speed signal. In addition or alternatively, an FMM device may convert an incoming high-speed signal into two or more corresponding outgoing low-speed signals.
Two or more FMM devices may be configured together for a variety of purposes. One such purpose is protection switching, where one or more protection FMM devices provide backup facilities in the event of a failure of one or more corresponding working FMM devices. Another purpose for configuring multiple FMM devices together is to provide a system that can simultaneously handle a multitude of incoming and outgoing signals.
Two FMM devices are configured together by connecting input/output (I/O) pins on one device to corresponding I/O pins on the other device. Pin count (i.e., the total number of I/O pins on a device) is a precious commodity in most integrated devices. When designing FMM devices, it is desirable to minimize the number of I/O pins that are used in configuring two (or more) FMM devices together.
In conventional SONET or SDH network-based communication systems, synchronous transport signals, such as STS-3c or STM-1, are mapped to or from corresponding higher-rate optical signals, such as a SONET OC-12 signal or an SDH STM-4 signal. The mapping of these and other synchronous transport signals to or from higher-rate optical signals generally occurs in a physical layer device commonly referred to as a mapper, which may be used to implement an add-drop multiplexer (ADM) or another node of a SONET or SDH communication system.
A need exists for improved framing synchronization control for a system with multiple mapper devices.